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Microbiology > Lectures 13&14: Pathogenicity of Microorganisms > Flashcards

Lectures 13&14: Pathogenicity of Microorganisms Flashcards

1
Q

Parasites are organisms that

A
  • Live on or within a host organism and are metabolically dependent on the host
  • are any organism that cause disease
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2
Q

The host is

A

larger organism that supports the survival and growth of a smaller organism

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3
Q

Infection

A
  • A parasite growing and multiplying within/on a host
  • may or may not result in overt infectious disease
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4
Q

Pathogen

A
  • Any parasite organism causing infectious disease
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5
Q

Primary (frank) pathogen

A

Causes disease by direct interaction with healthy host

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6
Q

Opportunistic pathogen

A

May be part of normal flora and causes disease when it has gained access to other tissue sites or host is immunocomprimised

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7
Q

Pathogenicity

A

ability to cause disease

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8
Q

Chain of events for a successful infection

A
  • agent identitiy
  • virulence of agent
  • means of exposure to agent
  • dose of agent
  • susceptibility of host to agen
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9
Q

infections passed from animal to human are termed

A

zoonoses

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10
Q

What does animate mean

A

from other humans or animals

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11
Q

what does inanimate mean

A

from water, soil, and food

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12
Q

Natural enviromental location in which the pathogen resides

A

Reservoir (can be animate or inanimate)

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13
Q

organisms that spread disease from one host to another

A

vector

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14
Q

infectious disease

A

infection with viruses, bacteria, fungi, protozoa, and helminths

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15
Q

Objective changes in body that can be directly observed

A

Signs

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16
Q

subjective changes experienced by patient

A

symptoms

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17
Q

Set of characteristic signs and symtpoms

A

disease syndrome

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18
Q

Incubation period

A

period after pathogen entry, before signs and symptoms

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19
Q

Prodromal stage

A
  • Onset of signs and symptoms
  • not clear enough for diagnosis
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20
Q

Period of illness

A
  • disease is most severe, signs and symptoms
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21
Q

Convalescence

A

Signs and symptoms begin to disappear

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22
Q

Course of infectious disease

A
  • Incubation period
  • Prodromal stage
  • Period of illness
  • Convalescence
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23
Q

A pathogen must contact a host and survive within it to cause a disease. To survive, it needs

A
  • A suitable environment
  • A source of nutrients
    • in competition with eukaryotic host cells
  • Protection from harmful elements
    • virulence factors allow a pathogen to oucompete host cells and resist their defenses
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24
Q

Some survival strategies for pathogens once in the host are

A
  • Adhesins
  • Enzymes
  • Toxins
  • Invasins
  • Autoinducers
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25
Q

Virulence factors determine the

A

degree to which a pathogen causes damage, invasion, infectivity

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26
Q

What is virulence

A

degree or intensity of pathogenicity

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27
Q

Virulence is determined in part by pathogen’s ability to

A
  • survive outside of host
    • more dependent on host (cannot survive outside of host)= less virulent
      *
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28
Q

What does pathogenicity islands mean

A
  • Major virulence factors on large segments on chromosomal or plasmid DNA
    • Increase bacterial virulence
    • absent in nonpathogenic members
    • common sequence characteristics
      • insertion-like seqquences for mobility
      • G + C content different from bacterial genome
      • several open reading frames
    • Can be spread through horizontal transfer of virulence genes to bacteria
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29
Q

What is the first step in disease

A
  • entrance and attachment
    • Portal of entry
      • Skin, respiratory, gastrointestinal, urogenital systems, or conjunctiva of eye, parental route (break in barrier defenses)
      • Vector borne, sexual contact, blood transfusion, or organ transplant
    • Adherence
      • medated by special molecules called adhesins
    • Colonization
      • A site of microbial reproduction on or within host
      • does not necessarily result in tissue invasion or damage
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30
Q

What are the adherence structures of microbes

A
  • Pili or fimbriae (adhesion molecules on bacterium’s cell surface) bind complementary receptor sies on host cell surface
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31
Q

what is microbial colonization site

A
  • Site of microbial reporduction on/in host
  • does not necessarily result in tissue damage
32
Q
  • Adhesin/ligans bind to receptors on host cells
    • examples on
      • Streptococcus mutans
      • Escherichia coli
      • Streptococcus pyogenes
A
  • Streptococcus mutans: Glycocalyx
  • Escherichia coli: Fimbriae
  • Streptococcus pyogenes: M protein
33
Q

Examples of microbial attachment mechanisms in Eschericia coli

A
  • Type I fimbrae ( leads to diarrhea and UTI)
  • P pili (leads to Hemolytic uremic syndrome)
34
Q

Adhesion mechanism of Streptococcus pyogenes

A
  • Protein F (causes strep throat)
35
Q

Attachement mechanism of streptococcus mutans

A

sugar residue/glycocalyx (causes dental caries)

36
Q

Infectivity

A

ability to create a discrete point of infection

37
Q

invasiveness

A

ability to spread to adjacent tissues

38
Q

Penetration can be active or passive explain both

A
  • active occurs through lytic substances which
    • attack the extracellular matrix and basement membranes of integuments and intestinal linings
    • degrade carbohydrate-protein complexes between cells
    • disrupts host cell surface
  • passive (e.g. Skin lesions, insect bites, wounds)
    • spread to deeper tissues involves production of specific products and/or enzymes that promote spreading
39
Q

Virulence factor produced by Staphylococcus aureus for bacterial pathogen invasion and dissemination

A

Coagulase: Coagulates (clots) the fibrinogen in plasma/ The clot protects the pathogen from phagocytosis and isolates it from other host defenses.

40
Q

Virulence factor produced by Groups A,B,C, and G streptococci, staphylococci, clostridia for bacterial pathogen invasion and dissemination

A

Hyaluronidase: hydrolyzes hyaluronic acid, a constituent of the extacellular matrix that cements cells together and render the intercellular spaces amenable to passage by the pathogen

41
Q

Virulence factor produced by Staphylococci, pneumonocci, and other streptococci for bacterial pathogen invasion and dissemination

A

Leukocidins: pore-forming exotoxins that kill leukocytes; cause degranulation of lysosomes within leukocytes, which decrease host resistance

42
Q

presence of viable bacteria in the blood

A

bacteremia

43
Q

Pathogens or their toxins in the blood

A

septicemia

44
Q

Invasiveness varies among pathogens. Examples

A
  • Clostridium tetani (tetanus) produces a number of virulence factors but is non-invasive
  • Bacillus anthracis (anthrax) and Yersinia pestis (plague) also produce many virulence factors and are highly invasive
  • Streptococcus spp. span the spectrum of virulence factors and invasiveness
45
Q

what is toxigenicity

A

ability to produce toxins

46
Q

What is a toxin

A

a specific substance that damages host

47
Q

Diseases that result from entry of a specific preformed toxin into host (Ex. Tetanus toxin)

A

Intoxications

48
Q

Toxemia

A

condition caused by toxins in the blood of host

49
Q

Exotoxins

A
  • Soluble, heat-labile, proteins
  • secreted into surroundings as pathogen grows
  • most exotoxin producers are gram-positive
  • often travel form site of infection to other tissues or cells where they exert their effects
  • Usually synthesized by specific bacteria that have toxin genes in their plasmids or prophage DNA
  • Among the most lethal substances known
  • Are highly immunogenic
  • Stimulate production of neutralizing Ab (antitoxins)
  • Chemically inactivated to form immunogenic toxoids
    • e.g. Tetanus toxoid
  • do not produce a fever (but they are heat labile)
  • LD50 is small
50
Q
A
51
Q

Types of Exotoxins

A
  • AB exotoxins
    • Composed of two subunits
      • A subunit- responsible for toxic effect
      • B subunit- binds to specific target cell
  • Specific host site exotoxins
  • Membrane-disrupting exotoxins
  • Superantigens
52
Q

Botulinum toxin

A
  • Organism:
    • Clostridium botulinum
  • Gene location:
    • Prophage
  • Toxin type:
    • AB
  • Mechanism of Action:
    • Blocks neurotransmitter release, leading to paralysis (flaccid paralysis)
    • specificially it attacks SNAP25 and Syntaxin and does not allow the Ach to be moved to the synaptic terminal and released into the synaptic cleft
53
Q

Tetanospasmin

A
  • Organism:
    • Clostridium tetani
  • Gene location:
    • Plasmid
  • Toxin type:
    • AB
  • Mechanism of Action
    • Blocks neurotransmitter, leadin to spastic paralysis
    • proteolysis of Synaptobrevin
54
Q

Superantigens

A
  • Stimulate about 30% of T cells of the immune system
    • Causes the T cells to overexpress and release cytokines
    • results in failure of multiple host organs allowing time for the microbe to disseminate
  • Example
    • Staphylococcal enterotoxin B
55
Q

Endotoxins

A
  • Lipopolysaccharide (LPS) in Gram-negative cell wall can be toxic to specific hosts
    • called endotoxin because it is an endogenous (part) of the bacterium and released when organism lyses
      • some is also released during multiplication
    • Toxic component is the lipid portion, lipid A
  • Heat Stable (but do produce fever)
  • Toxic (nanogram amounts)
  • Weakly immunogenic
  • Generally similar, despite source
  • Cause general system effects
    • Fever, weakness, diarrhea, inflammation, intestinal hemorrhage, and fibrinolysis, the enzymatic breakdown of fibrin, the major protein component of blood clots
    • Bring about these effects indirectly:
      • endotoxin interacts with host molecules and cells, activating host systems
        • coagulation, complement, fibrinolytic, and kininogen system
      • e.g. interaction with macrophages—> release of endogenous pyrogen (induces fever)
      • e.g. binding to LPS-binding protein —> release of cytokines
        • tumor necrosis and others lead to septic shock
  • LD50 is relatively large
  • chemistry:
    • lipid
  • Source:
    • Gram-negative
  • Not neutralized by antitoxin
56
Q

Mycotoxins

A
  • Secondary metabolites of fungi
    • common contaminants of food crops
    • Aspergillus flavus and A. parasiticus produce carcinogenic aflatoxin
    • Stachybotrys produce tissue-damaging satratoxins
    • Claviceps purpurea (ergot) produce hallucinogen lysergic acid (LSD)
57
Q

effects of pathogen biofilm growth

A
  • May cause a chronic infection
  • increases virulence
  • become less sensitive to antibiotics
  • make cells in biofilm more resistant to host defense (“frustrates” phagocytes)
58
Q

Cell wall components of pathogens that are increase virulence

A
  • M protein resists phagocytosis
    • ex. Streptococcus pyogenes
  • Opa protein inhibits T helper cells
    • Ex. Neisseria gonorrhoeae
  • Mycolic acid (Waxy lipid) resists digestion
    • Ex. Mycobacterium tuberculosis
59
Q

Resisting host defenses

A
  • Production of decoy proteins to bind available neutralizing antibodies
  • Lengthened O-chains to prevent host detection or lysis
  • some survive inside host cells
    • eject themselves form cell to cell using host actin
    • ex. Shigella sp. and Rickettsia sp.
  • Infection of immune system cells, diminishing function
  • Fuse with adjacent cells to prevent exposure to antimicrobial proteins in host
  • Capsules prevent phagocytosis
  • Mutations change antigenic sites or alter expression of antigens
    • thourhg downregulation or phase variation (ex. Altered Pilin protein, N. gonorrhea)
  • Produce substances that resemble host tissue
  • Produce proteases that degrade host proteins
  • Special proteins that interfere with host defenses
60
Q

Examples of Capsules and function

A
  • Prevent phagocytosis
    • Streptococcus pneumoniae
    • Haemophilus influenzae
    • Bacillus anthracis
    • Staphylococcus aureus
61
Q

Pathogen Enzymes

A
  • Coagulase
    • Coagulates fibrinogen
  • Kinases
    • Digest fibrin clots
  • Hyaluronidase
    • Hydrolyzes hyaluronic acid (found in CT)
  • Collagenase
    • Hydrolyzes collagen
  • IgA proteases
    • Destroy IgA antibodies
62
Q

Evidence suggests correlation between mode of transmission and degree of virulence

A
  • Direct contact
    • less virulent
  • Vector-borne
    • highly virulent in human host; relatively benign in vector
  • Greater ability to survive ouside host
    • means more virulent
63
Q

What is Tropism

A
  • Tropism
    • Pathogen must make contact with appropriate host tissue
      • determined by specific cell surface receptors
  • (note that transmission alone is not enough for infection to occur)
64
Q
A
65
Q

What are the five main modes of transmission

A
  • Airborne (indirect)
  • contact
  • vehicle (indirect)
  • vector borne
  • vertical
66
Q
A
67
Q

inanimate materials or objects involved in pathogen transmission

A

Vehicles

68
Q

Fomites

A

Common vehicle such as surgical instruments, bedding, and eating utensils

69
Q

What is the difference between harborage transmission and biological transmission

A
  • Both are types of internal transmission for vector-borne transmission
  • Harborage transmission
    • pathogen does not undergo changes within vector
  • Biologic transmission
    • pathogen undergoes changes within vector
70
Q

Occurss when the unborn child aquires a pathogen form an infected mother

A

Vertical transmission

71
Q

Examples of congential infection (born with infection)

A
  • gonorrhea (especially in the eyes)
  • herpes
  • german measles
  • toxoplasmosis
72
Q

What is infectious dose 50

A

Dose that causes 50% of the host organisms to become infected

73
Q

Infectious dose 50 for Bacillus anthracis in each of the 3 portals of entry

A
  • ID50 through skin:
    • is 10-50 endospores
  • ID50 through inhalation:
    • is 10,000 to 20,000 endospores
  • ID50 through GI is 250,000-1,000,000 endospores
74
Q

Cytopathology

A
  • Can be used to observe cells in tissue culture for death rates rather than entire organisms
75
Q

What are the two main factors of host susceptibility

A
  • Defense mechanisms of host (innate and adapted/acquired immunity)
  • Pathogenicity of pathogen
  • (note that nutrition, genetic predisposition, and stress also play a role in host susceptibility to infection)
76
Q

What are the portals of exit for a pathogen

A
  • Respiratory tract
    • coughing and sneezing
  • Gastrointestinal tract
    • Feces and saliva
  • Genitourinary tract
    • urine and vaginal secretions
  • Skin
  • Blood
    • biting arthropods and needles or syringes
77
Q
A

Microbiology (16 decks)

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